In cases where solid fuel is wood, it has been found that combustion in conventional furnaces encounters many problems such as short duration and irregularity of heat dissipation, formation of creosote at low operating conditions, and a certain difficulty in controlling combustion. Conventional solution in solving these problems includes the combined heating of wood, oil, gas and electricity, the accumulation of a heat reserve or automatic feeding units. However, these systems present inconveniencies such as elevated costs, the taking of large space area, insufficient combustion at low operating conditions; and, the control of combustion is still difficult to achieve. Furthermore, in the case of a heat reserve, the reaction time is still relatively long.